Tea polyphenols - antioxidants or prebiotics?

Polyphenols in tea may preferentially suppress the growth of
pathogenic bacteria in the gut, but not the growth of 'friendly'
bacteria, says a new study from Singapore.

"It is generally believed that possible beneficial health
effects of tea polyphenols are due to their anti-oxidant
activity,"​ wrote lead author Hui Cheng Lee from the National
University of Singapore.

"Evidence from our study indicates that phenolics are likely
to benefit the host by inhibiting pathogen growth and regulating
commensal bacteria, including probiotics, and could therefore be
considers as prebiotics."​

The health benefits of tea ranging from a lower risk of certain
cancers to weight loss, and protection against Alzheimer's, have
been linked to the polyphenol content of the tea. Green tea
contains between 30 and 40 per cent of water-extractable
polyphenols, while black tea (green tea that has been oxidized by
fermentation) contains between 3 and 10 per cent. Oolong tea is
semi-fermented tea and is somewhere between green and black
tea.

The four primary polyphenols found in fresh tealeaves are
epigallocatechin gallate (EGCG), epigallocatechin, epicatechin
gallate, and epicatechin.

The new study, published in the Elsevier journal Research in
Microbiology​, looked at the effects of 31 different phenolics
extracted from Yunnan Chinese tea on the growth of 28 different
bacteria, including pathogenic, commensal (normal), and probiotics
found in the intestine. These included strains of the aerobic
pathogens E. coli, Salmonella, and Listeria​, and probiotic
Lactobacillus​ strains, and strains of the anaerobic
pathogens Bacteroides​ and Clostridium​, and probiotic
Bifidobacterium​ strains.

Cells were cultured in the presence of 0.1 per cent polyphenols
at 37 degrees Celsius for 24 hours.

"Our data demonstrate that phenolic compounds have general
inhibitory effects on intestinal bacteria. The level of inhibition
varies depending on the bacterial species and chemical structure of
the compound,"​ wrote Lee.

Indeed, growth of the pathogenic E. coli and Salmonella
typhimurium​ were most strongly inhibited by the tea polyphenols
and their metabolites, as were strains belonging to the
Bacteroides​ and Clostridium​ genera.

However, the researchers report that the growth of the probiotic
Bifidobacterium​ and Lactobacillus​ strains were less
affected by the tea compounds.

"Since probiotic growth was relatively unaffected by most of
the aromatic compounds tested, probiotic colonization in the
intestine should continue in the presence of phenolics so as to
improve the intestinal microbial balance and inhibit pathogen
growth,"​ said the researchers.

"Although not fully comprehensive, this in vitro study
indicates a substantial number of complex interactions between
intestinal bacteria, phenolics and their metabolism,"​ they
said.

They called for more research to further investigate the
influence of the tea polyphenols on gut microflora, and the overall
maintenance of human health and disease prevention, and said that
the research suggests that the antioxidants may also be
prebiotic.

Prebiotic ingredients, or those that boost the growth of
beneficial probiotic bacteria in the gut, are worth about €90
million in the European marketplace but are forecast to reach
€179.7 million by 2010, according to Frost & Sullivan.

The market has been largely created by three inulin producers,
all based in Europe, but other ingredient manufacturers are
increasingly looking to promote the prebiotic effect of their
products as evidence suggests that prebiotics could be even more
useful than the probiotic bacteria that they feed.